An SF may include one or more stages of switch elements, as shown in FIG. 1, FIG. 2, FIG. 3, and FIG. 4. The SF shown in FIG. 1 and FIG. 2 includes a stage-0 switch element (S0) and multiple line cards (LCs). The SF shown in FIG. 3 and FIG. 4 includes three stages of switch elements and multiple LCs. In FIG. 1 and FIG. 3, the LC that sends uplink data flows (ingress LC) is located on one side of the switch element, and the LC that receives downlink data flows (egress LC) is located on the other side of the switch element. The LC in FIG. 2 and FIG. 4 can send uplink data flows and receive downlink data flows. In FIG. 4, the S1/3 includes two parts: a stage-1 switch element (S1), and a stage-3 switch element (S3). The packets sent by a source LC carry destination LC information. The packets pass through the S1, a stage-2 switch element (S2), and S3, and arrive at the destination LC. The packets include variable-length packets and fixed-length cells.
In a common multi-stage SF, both the LC and the S1/3 are generally located in a line card chassis (LCC). The S1/3 includes two parts: the S1, and the S3, where the S1 corresponds to the S3. In this case, the S1 and S3 may be located on the same physical component or on different physical components. The 81 may be coupled to the S3 through a specific interface; the S2 is generally located in a fabric card chassis (FCC), and the FCC is coupled to the LCC through fibers or cables, as shown in FIG. 5. According to a specific algorithm such as a load balancing algorithm, the S1 in the LCC selects an S2, and forwards the packets sent by the source LC to the FCC through fibers, and a repeater (RPT) in the FCC forwards the packets to the S2. The S2 switches the packets to the S3 in the LCC according to the destination LCC information carried in the packets. Finally, the S3 in the destination LCC switches the packets to the destination LC according to the destination LC information carried in the packets. The FCC may have no RPT.
The defects of the prior art are as follows:
In a multi-stage SF provided in the prior art, flow control information is not responded to in time. For example, when congestion occurs at the S3, and the S3 wants to notify its upstream switch element (such as the S2) to suspend the sending of packets, the physical path of flow control information fed back by the S3 to the S2 is as follows: The S3 transmits the flow control information to the S1 which is corresponding to the S3, and the S1 sends the flow control information to the S2. When congestion occurs at the S2, the physical path of flow control information fed back by the S2 to the upstream switch element (such as the S1) is as follows: The S2 transmits the flow control information to the S3, and the S3 sends the flow control information to the S1. Therefore, the flow control information fed back by a downstream switch element to an upstream switch element needs to pass through fibers between the FCC and the LCC, the transmission of flow control information in the fibers incurs a great delay, and the fed back flow control information is not responded to in time.